Designating targets using laser spots is a widely known technique due to high precision of the pointing laser device and the relatively low cost of the homing head (or seeker). For example a seeker can be mounted on an intercepting platform, such as a missile, and utilize the energy reflected from an illuminated target, for generating steering commands and homing the intercepting platform towards a target.
As illustrated schematically in FIG. 1, according to known laser spot guiding techniques, a laser designator 1 constantly tracks the target 3 and illuminates it with a pulsed spot laser beam 4. FIG. 1 also illustrates an intercepting platform 5 (in this case a missile) employing a seeker with a laser sensor. The sensor's surface is often divided into four equal sectors (not shown in FIG. 1) and associated with a spectral filter which transfers energy reflected from the illuminated target as well as a certain portion of noise (that can stem e.g. from sunlight). The energy received in each of the sectors of the sensor is converted into corresponding signal intensity. The differences between the signal intensities in the respective sectors are used to calculate the direction to the target (line of sight—LOS 6) and/or the change of direction LOS rate. The calculated LOS and/or LOS rate serve for steering the missile for homing onto the target 3.
Publications considered to be relevant as background to the presently disclosed subject matter are listed below. Acknowledgement of the references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.
US Patent Application, Publication No. US2013087684 discloses a laser designator system using modulated CW laser diodes and a conventional high pixel count image sensor array, such as CCD or CMOS array. These systems filter the laser signal spatially, by collecting light over a comparatively long period of time from a very few pixels out of the entire field of view of the image sensor array. This is in contrast to the prior art systems where the laser signal is filtered temporarily, over a very short time span, but over a large fraction of the field of view. By spatially filtering the signal outputs of the individual pixels, it becomes possible to subtract the background illumination from the illuminated laser spot.
EP Patent Application, Publication No. 0770884 discloses a process which includes sensitivity to spatial solar noise which masks the detection of a target. After formation of an image of the scene containing an image of the target which is illuminated by a laser beam forming an illuminated spot, and focusing of this image, the illuminated spot is detected. Detection is carried out by continual transfer of charges in a CCD matrix, the charges being freed by photon conversion from the incident light flux with a limited exposure time. The system includes an objective focusing on to a matrix detector with pixels (Pi), integrated with a multiplexing circuit (C) coupled to an output shift register (R). This is linked to an amplification stage (A) and a processing unit (5) comprising a sequencer for applying charge transfer signals to the detector and to the output register.